Polyolefins have long been used in the manufacture of many everyday products such as films and fibers. It is known to incorporate small amounts of additives into polyolefin compositions to improve processing, and in some instances, the resulting product's characteristics. The additives can sometimes include other polymers.
Polyolefin films are not easily printable. This limits their utility in areas where printable surfaces are desired. Methods to improve printability of polyolefin are known. These methods include flame treatment, plasma treatment, chemical treatment and corona discharge treatment. These treatments can soften or ionize the surface of polyolefins and make the surface temporarily printable.
U.S. Pat. No. 5,330,831 teaches how to modify a polypropylene substrate by corona discharge treatment and then cover the treated surface with a coating. The coating is a printable polymer and, therefore, the coated polypropylene is printable. Similarly, U.S. Pat. Nos. 5,789,123, 5,496,635, 5,496,636, 4,732,786, and 5,827,627 also teach polypropylene films that are coated with printable coatings.
Another method to make polypropylene substrates printable is to make multilayer films. For example, U.S. Pat. No. 5,902,684 teaches a printable multilayer film that consists of a polypropylene layer, a primer coating layer, a layer of crosslinked polyvinyl alcohol, and a layer of a blend of polyvinyl alcohol and an ethylene-acrylic acid copolymer. A printable outer layer makes the multilayer film printable. Polypropylene films with multilayers or coated with printable coatings, although printable, are difficult and expensive to make. Moreover, these modifications often impair the clarity of polypropylene films.
Sealability of polyolefin films is often desired. Sealing aids, such as EVA, are often used with polyolefin films to render them heat-sealable.
With regard to fibers, adding a small amount of a polymer capable of forming an anisotropic melt with a fiber-forming polymer in the temperature range at which fibers are spun is disclosed in U.S. Pat. Nos. 4,442,057 and 4,442,266. The additive polymers are liquid crystal polymers such as copolymers of 6-oxy-2-naphthoyl and p-oxybenzoyl moieties. Fiber-forming polymers to which the additive polymers can be added include polyesters, polyamides and polypropylene.
U.S. Pat. No. 4,518,744 discloses an improved melt spinning process and fibers obtained by the addition of 0.1 to 10 wt. % of a polymer that is immiscible in a melt of common fiber-forming polymers such as polyesters, copolyesters, polyamides, copolyamides and polyolefins. While the immiscible polymers can be from the same chemical family as the fiber-forming polymer, the immiscible polymer must have an extensional viscosity such that molten spheres of the additive polymer deform into microfibrils along the spinning threadline.
Imidated polyalkyl methacrylate is added to polyethylene terephthalate at a 0.1 to 5 wt. % level in U.S. Pat. No. 5,565,522 to improve spinning and reduce thread break.
The inability to dye polyolefin fibers is also well known and has been a long-standing problem within the industry. Polyolefins are hydrophobic and they lack dye sites to which dye molecules may become attached. One approach to color polyolefin fibers has been to add colored inorganic salts or stable organometallic pigments to polymer melts prior to spinning. Nonvolatile acids or bases or materials such as polyethylene oxides or metal salts have also been added to polymers prior to fiber formation to increase the affinity of the fiber for disperse, cationic, acid or mordant dyes. Still another approach has been to chemically graft polyolefin fibers with appropriate monomers after fiber formation to improve dyeability. See Textile Fibers, Dyes, Finishes, and Processes: A Concise Guide, by Howard L. Needles, Noyes Publications, 1986, page 191.
Efforts to impart dyeability to polyolefins, and particularly polypropylene, by incorporating nitrogen-based polymer additives have also been disclosed. In U.S. Pat. No. 3,361,843, various incompatible, basic nitrogen-based polymers are added to polypropylene, given a treatment with high concentrations of certain acidic chemical reagents and then dyed in an acid dye bath. According to U.S. Pat. No. 3,653,803, dyeing of the polypropylene fiber is somewhat improved by the method of U.S. Pat. No. 3,361,843, but processing of the fiber is difficult due to polymer incompatibility, the dye fastness properties not being reliably reproducible, and tinctorial strengths not being commercially sufficient. In U.S. Pat. Nos. 3,395,198 and 3,653,803, various compatible nitrogen-containing copolymers of ethylene and an aminoalkyl acrylate compound are disclosed. When blended with polyolefins, the copolymers render fibers formed from the blend acid dyeable. In U.S. Pat. No. 5,017,658, a fiber finishing agent is used in melt spinning dyeable polypropylene fibers obtained by blending a copolymer of an ethylene aminoalkyl acrylate with polypropylene.
Also due to their hydrophobic nature, polyolefin fibers have been found to be relatively non-wettable. This has proven to be an obstacle in their use as wipes since their hydrophobic nature tends to make the incorporation of water-based chemicals into the fibers difficult. This has also proven to be an obstacle for the use of polyolefin fiber in the manufacture of other products such as those used in filtration applications, and dyed and printed fabrics.
Accordingly, it would be advantageous to provide a polyolefin composition that could be used to manufacture common polyolefin products, such as polyolefin films and polyolefin fibers, that overcomes at least one deficiency associated with the prior art. More specifically, it would be desirable to provide a polyolefin composition that can also be used to manufacture printable polyolefin films with good heat seal properties. Also, it would be desirable to provide polyolefin compositions that can be used to manufacture fibers that are dyeable and wettable.